Great question — answering as the UphillTech team:
Here is a good Microsoft Article for doing that. This is a fairly long and technical article. As I noted at the end, Virtual Machines are better, but if you wish to try this, make sure you read the entire article. Dual Boot Win 7 after Windows 10 Your PC may refuse to boot and or unexpected PC crashes could damage or even delete your files, so you should create an Image backup your Windows 10 installation before you proceed to install Windows 7. If you purchased a new computer with Windows 10 preinstalled then check your manufacture’s support web site to see if there are Windows 7 (or 8.1) device drivers available. The lack of device drivers is a good indication that your new computer is...
Full answer by anon: https://superuser.stackexchange.com/a/1694399 (CC BY-SA 4.0).
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